i) Field of the Invention
The present invention relates to a connection structure of circuit boards having electronic parts thereon such as a thermal printer head, a head board in an image sensor or the like and a flexible cable for coupling the circuit boards, and more particularly to a connection structure of at least two circuit boards having various electronic parts mounted on their surfaces and various wiring circuits formed thereon and a flexible cable haivng a belt form for electrically coupling the circuit boards and a connection method using the same.
ii) Description of the Related Arts
Conventionally, in one case, in order to electrically connect wiring circuits formed on at least two circuit boards, a connector is attached to the wiring circuit of each circuit board by soldering, and the connectors of the two circuit boards are mutually connected. In another case, lead terminals are connected to the wiring circuit of one circuit board by soldering, and the ends of the lead terminals are connected to the wiring circuit of another circuit board by soldering. In still another case, the wiring circuits of the two circuit boards are directly connected to each other by soldering.
Further, in general, two circuit boards are electrically connected to each other by using a flexible cable. In this case, the connectors are attached to the wiring circuits of the circuit boards by soldering, and connectors attached to both ends of the flexible cable are inserted into the connectors of the circuit boards. In another case, a direct connection of the flexible cable with the wiring circuits of the circuit boards soldering is also generally carried out.
However, usually, in order to electrically connect at least two circuit boards by using a flexible cable, a connector should be attached to each circuit board. Hence, much time and labor are required for the connection of the connectors with the circuit boards. Thus, not only is the cost for carrying out the connection largely raised but also the connection parts themselves are extremely costly.
Also, all the above-described connection means require soldering, and an improper thermal influence is given to the various electronic parts mounted on the surfaces of the circuit boards. Further, droplets or splashes of solder and flux can be attached to the various electronic parts and the various wiring circuits.
Conventionally, for example, an improved connection structure for coupling circuit boards by a flexible cable without using soldering has been proposed, as disclosed in Japanese Patent Laid-Open No. Hei 2-22890.
In this connection structure, the flexible cable positioned and held on the circuit boards is crimped onto the circuit boards by using silicone rubber or the like, and thus the electrical connection between the circuits of the circuit boards can be exactly performed without using soldering.
Therefore, in this connection structure without using soldering, even when an electric circuit connection part, an exothermic resistor part and a light emitter or a light detector are present in close proximity to one another on the circuit boards as in a thermal printer head board or an image sensor, the improper thermal influence exerted by the soldering operation and the droplets or splashes of solder or flux will not be given to the exothermic resistor part, the light emitter or the light detector.
However, in this conventional structure, when two circuit boards are arranged in a laminated fashion, an exact electrical connection between the two circuit boards in a simple structure can not be performed.
Conventionally, this two-layer laminate circuit board unit is often used for containing complicated wiring patterns and electronic parts within a limited area. For instance, within an image sensor board or the like, since an array of a plurality of light detector elements and amplifying elements can not be coexistent within the same flat surface, these elements are mounted on two boards in a separate structure. That is, the light detector element array is arranged on a first board on the surface side, and the amplifying elements are mounted on a second board on the reverse side. In order to perform an electrical connection of these separated two boards, the two boards are usually laminated and are electrically connected with each other by using one of the several above-described methods.
Accordingly, in such a stacked two-layer circuit board unit, in particular, the connection parts are enlarged. Further, for the electrical connection of the two boards by using one flexible cable, the aforementioned crimp structure using the silicone rubber can not be used.